1. Field of the Invention
This invention relates to a gas injector which provides an improved signal to noise ratio when applied to a sensitive analytical instrument.
2. Description of the Related Art
The carrier gas that passes through a conventional gas injector can be contaminated easily due to air leaks or gases emitting from polymers and other internal surfaces of the injector. The contaminated carrier gas creates a high baseline noise when injected into a sensitive analytical instrument, therefore reducing the signal to noise ratio. Examples of sensitive analytical instruments include, but are not limited to, gas chromatographs, mass spectrometers or ion mobility spectrometers.
FIGS. 1 and 2 illustrate how the carrier gas becomes contaminated when passing through a conventional gas injector. The gas injector in FIGS. 1 and 2 comprises a six-port switching valve which has, in the clockwise order, ports 1, 2, 3, 4, 5 and 6. In FIG. 1, the switching valve is at the sample loading position. The carrier gas can flow through ports 1 and 2 to an analytical instrument. At the same time, a gaseous sample can be loaded to a sample gas channel through ports 5 and 6. The waste in the sample gas channel can be driven out of the sample gas channel through ports 3 and 4. Air leaks through the seals of ports 1 and 2, as well as gases emitting from the internal surfaces of the injector, contaminate the carrier gas when the carrier gas flows through the injector. The contaminated carrier gas enters the analytical instrument and creates a high baseline noise.
FIG. 2 shows the conventional gas injector at the sample injecting position. The carrier gas can be directed through, in the consecutive order, port 1, port 6, the sample gas channel, port 3 and port 2 to the analytical instrument, sweeping the gaseous sample in the sample gas channel to the analytical instrument.
Traditionally, contaminations by air leaks can be reduced by enclosing the gas injector in a container purged with the same type of gas as the carrier gas. Contaminations by the internally released gases can be minimized by limiting the upper temperature at which the gas injector operates.
Accordingly, there is a need to provide a gas injector which does not require externally purged enclosure and which is easy to make and use. There is also a need to make a gas injector which can operate at high upper temperatures and has a low baseline noise.
It is therefore an object of the present invention to produce a gas injection device which has a low baseline noise and a high signal to noise ratio.
It is another object of the invention to make a gas injection device which does not require externally purged enclosure and can be used at high upper temperatures without losing the high signal to noise ratio.
It is further an object of the invention to make a gas injection device which is easy to make and use.
In accordance with one aspect of the invention, the gas injection device comprises (1) a carrier gas channel through which a gas is capable of entering the device, (2) an output channel through which the gas can leave the device, (3) a first purge channel, (4) a sample gas channel capable of holding a gaseous sample and (5) a switch structure. The switch structure can be a multi-port switching valve, or an assembly of discrete switches such as pneumatic switches. Other flow controlling devices or switching mechanism can also be used as a switch structure, as appreciated by one of skill in the art. The switch structure has at least a first position and a second position. When the switch structure is at the first position, the carrier gas channel connects to the output channel through the sample gas channel and the first purge channel. When the switch structure is at the second position, the sample gas channel disconnects to the carrier gas channel, the output channel and the first purge channel, and the carrier gas channel connects to (1) a first vent environment through the first purge channel and (2) the output channel.
In accordance with another aspect of the invention, the gas injection device further comprises a second purge channel and a connecting channel. The carrier gas channel connects to the output channel through the connecting channel. When the switch structure is at the first position, the carrier gas channel also connects to the output channel through, in the consecutive order, the first purge channel, the sample gas channel and the second purge channel. When the switch structure is at the second position, the sample gas channel disconnects to the carrier gas channel, and the carrier gas channel connects to a second vent environment through, in the consecutive order, the connecting channel and the second purge channel.
In accordance with yet another aspect of the invention, the gas injection device comprises a first vent channel and a second vent channel. When the switch structure is at the second position, the carrier gas channel connects to the first vent environment through, in the consecutive order, the first purge channel and the first vent channel, and the carrier gas channel connects to the second environment through, in the consecutive order, the connecting channel, the second purge channel and the second vent channel. When the switch structure is at the first position, the carrier gas channel disconnects to the second vent channel, and preferably, the carrier gas channel disconnects to both the first and the second vent channels.
In one embodiment of the invention, the pneumatic restriction of the connecting channel is greater than the sum of the pneumatic restrictions of the first purge channel, the sample gas channel and the second purge channel.
In another embodiment of the invention, the first and the second vent environments are the atmosphere.
In a preferred embodiment of the invention, the switch structure of the gas injection device comprises a 8-port switching valve comprising, in the clockwise order, ports 1, 2, 3, 4, 5, 6, 7 and 8. When the switch structure is at the first position, the carrier gas channel connects to the output channel through, in the consecutive order, the first purge channel, port 7, port 6, the sample gas channel, port 3, port 2 and the second purge channel. When the switch structure is at the second position, the carrier gas channel connects to the first vent environment through, in the consecutive order, the first purge channel, port 7, port 8 and the first vent channel, and the carrier gas channel connects to the second vent environment through, in the consecutive order, the connecting channel, the second purge channel, port 2, port 1 and the second vent channel.
In another preferred embodiment, the switch structure comprises a 6-port switching valve. When the switch structure is at the first position, the carrier gas channel connects to the output channel through, in the consecutive order, the first purge channel, port 5, the sample gas channel, port 2 and the second purge channel. When the switch structure is at the second position, the carrier gas channel connects to the first vent environment through, in the consecutive order, the first purge channel, port 5, port 6 and the first vent channel, and the carrier gas channel connects to the second vent environment through, in the consecutive order, the connecting channel, the second purge channel, port 2, port 1 and the second vent channel.
In accordance with another aspect of the invention, the switch structure comprises three pneumatic switches. When the switch structure is at the first position, the carrier gas channel connects to the output channel through, in the consecutive order, the first purge channel, the first pneumatic switch, the sample gas channel, the second pneumatic switch and the second purge channel, and the second purge channel disconnects to the second vent environment. When the switch structure is at the second position, the carrier gas channel disconnects to the sample gas channel, and the carrier gas channel connects to the second vent environment through, in the consecutive order, the connecting channel, the second purge channel, the third pneumatic switch and the second vent channel.
In accordance with yet another aspect of the invention, the output channel connects to an analytical instrument. The analytical instrument may be a gas chromatography, a mass spectrometer or an ion mobility spectrometer.
In accordance with one aspect of the invention, a method is provided for introducing a gaseous sample to an analytical device. The method comprises the steps of (a) directing a carrier gas to the first vent environment through, in the consecutive order, the carrier gas channel and the first purge channel, and directing the gaseous sample to the sample gas channel, wherein the switch structure is at the second position; and (b) changing the switch structure from the second position to the first position and directing the carrier gas to the output channel through, in the consecutive order, the carrier gas channel and the sample gas channel.
In accordance with another aspect of the invention, the method for introducing a gaseous sample to an analytical instrument comprises the steps of: (a) directing a carrier gas to the first vent environment through, in the consecutive order, the carrier gas channel and the first purge channel, directing the carrier gas to the second vent environment through, in the consecutive order, the carrier gas channel, the connecting channel and the second purge channel, and directing the gaseous sample to the sample gas channel, wherein the switch structure is at the second position; and (b) changing the switch structure from the second position to the first position and directing the carrier gas to the output channel through, in the consecutive order, the carrier gas channel, the first purge channel, the sample gas channel and the second purge channel.
In accordance with yet another aspect of the invention, the method for introducing a gaseous sample to an analytical instrument comprises the steps of: (a) directing a carrier gas to the first vent environment through, in the consecutive order, the carrier gas channel, the first purge channel and the first vent channel, directing the carrier gas to the second vent environment through, in the consecutive order, the carrier gas channel, the connecting channel, the second purge channel and the second vent channel, and directing the gaseous sample to the sample gas channel, wherein the switch structure is at the second position; and (b) changing the switch structure from the second position to the first position and directing the carrier gas to the output channel through, in the consecutive order, the carrier gas channel, the first purge channel, the sample gas channel and the second purge channel.
In one embodiment, the gas injection device comprises an input means for channeling a gas into the device, an output means for channeling the gas out of the device, a first purge channel, a holding means for holding a gaseous sample, and a switching means for regulating connections among the holding means, the input means and the output means. The switching means has at least an open state and a close state. When the switching means is at the open state, the gas is capable of being channeled from the input means through the first purge channel and the holding means to the output means. When the switching means is at the close state, the holding means disconnects to the input means and the output means, and the gas is capable of being channeled to (1) a first vent environment through, in the consecutive order, the input means and the first purge channel and (2) the output means through the input means.
In another embodiment, the device further comprises a second purge channel and a connecting means for connecting the input means to the output means. When the switching means is at the open state, the gas is capable of being channeled through, in the consecutive order, the input meaning, the first purge channel, the holding means and the second purge channel to the output means. When the switching means is at the close state, the holding means disconnects to the input means, and the gas is capable of being channeled through, in the consecutive order, the input means, the connecting means and the second purge channel to a second vent environment.
In a preferred embodiment, the pneumatic restriction of the connecting means is greater than the sum of the pneumatic restrictions of the first purge channel, the holding means and the second purge channel.
In accordance with a further aspect of the invention, the switch structure of the gas injection device of the invention comprises a first switch and a second switch. When the switch structure is at the first position, the carrier gas channel connects to the output channel through, in the consecutive order, the first switch, the sample gas channel and the second switch. In one embodiment, the switch structure comprises a switching valve which comprises a plurality of ports. Each of the first and the second switches comprises at least one of said plurality of ports.